CDMA base station having an improved antenna system

ABSTRACT

A CDMA base station includes an antenna system having multiple antennas and delay units for receiving a transmitted signal and outputting a combined signal having a known distortion imparted by the antenna system. The combined signal is in turn processed by a modem, which compensates for the known distortion in a manner which provides improved signal gain. The improved signal gain permits a reduction in transmit power and, accordingly, increased capacity of the base station. Where the antenna system is to be remotely located from related signal processing equipment, separate units for the RF receiver/transmitter and the other signal processing equipment are provided so that the RF receiver/transmitter may also be remotely located along with the antenna system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/854,725;filed on May 14, 2001; which is a continuation of application Ser. No.08/961,482; filed on Oct. 31, 1997, which issued as U.S. Pat. No.6,259,687 on Jul. 10, 2001.

BACKGROUND

The present invention relates to wireless digital communication systems.More particularly, the present invention relates to communicationstations which employ code-division multiple access (CDMA) technologywherein the station has multiple antennas for increasing the capacity ofthe CDMA system.

Over the last decade consumers have become accustomed to the convenienceof wireless communication systems. This has resulted in a tremendousincrease in the demand for wireless telephones, wireless datatransmission and wireless access to the Internet. The amount ofavailable RF spectrum for any particular system is often quite limiteddue to government regulation and spectrum allotments. Accordingly, theneed to utilize one's allocated RF spectrum efficiently is desired.

CDMA communication systems have shown promise in the effort to provideefficient utilization of the RF spectrum. At least one brand of CDMAsystems, Broadband Code Division Multiple Access™ or B-CDMA™communication systems available from InterDigital CommunicationsCorporation, permit many communications to be transmitted over the samebandwidth, thereby greatly increasing the capacity of the RF spectrum.In B-CDMA™ brand communication systems, an information signal at thetransmitter is mixed with a pseudo random “spreading code” which spreadsthe information signal across the entire bandwidth which is employed bythe communication system. The spread signal is upconverted to an RFsignal for transmission. A receiver, identified by the pseudo randomspreading code, receives the transmitted RF signal and mixes thereceived signal with an RF sinusoidal signal generated at the receiverby a first-stage local oscillator to downconvert the spread spectrumsignal. The spread information signal is subsequently mixed with thepseudo random spreading code, which has also been locally generated, toobtain the original information signal.

In order to detect the information embedded in a received signal, areceiver must use the same pseudo random spreading code that was used tospread the signal. All signals which are not encoded with the pseudorandom code of the receiver appear as background noise to the receiver.Accordingly, as the number of users that are communicating within theoperating range of a particular communication station increases, theamount of background noise also increases, making it difficult forreceivers to properly detect and receive signals. The transmitter mayincrease the power of the transmitted signal, but this will increase thenoise (interference) as seen by other receivers.

Applicants have recognized the need to decrease the amount ofinterference in order to increase the capacity (number of users) of theCDMA system.

SUMMARY

A communication station for use in a CDMA communication system isprovided with an antenna system which includes a plurality of antennasfor receiving CDMA communication signals. The antennas are coupled to asummer, which outputs a summed signal from the antenna system. One ofthe antennas is directly coupled to the summer. Each of the otherantennas is coupled to a respective delay unit which imparts apredetermined fixed delay to the signals received by the respectiveantennas. Each delay unit is in turn coupled to the summer. The antennasystem, accordingly, outputs a summed signal which has a known phasedistortion corresponding to the fixed delays imparted by the delayunits.

A receiver is coupled to the antenna system summer output, strips thecarrier frequency, and passes the resultant summed baseband signal toone or more modems. Where the communication station is designed toreceive communications associated with a single dedicated CDMA code,such as a subscriber station, a single modem is preferred. Wheremultiple communications are to be simultaneously processed, such as in abase station or a subscriber unit which serves multiple users or as anemulated base station, multiple modems are provided.

Each modem is configured to receive an individual communication signalcontained within the baseband signal associated with unique CDMA codes.The modems include circuitry for compensating for at least the knownsignal phase distortion imparted by the delay units. Preferably, eachmodem includes a vector correlator (also known as a rake receiver) fordetermining filter coefficients which are passed to an adaptive matchedfilter (AMF). The AMF is a transversal filter which uses thecoefficients to overlay delayed replicas of the signal onto each otherto provide a filtered signal having increased signal-to-noise ration(SNR).

The vector correlator/rake receiver has a sufficient capacity todetermine filter coefficients over a window of time which is at least aswide as the known delays created by the antenna system. Preferably,three antennas are used, first, second and third. The second antenna'ssignal is delayed to provide a signal replica with a three-chip delayrelative to the signal replica provided by the first antenna. The thirdantenna's signal is delayed to provide a signal replica having aseven-chip delay relative to the signal replica provided by the first.In order to process the delayed replicas of the signal which originatedwith the second and third antennas, the vector correlator/rake receiverprocesses information in at least an eleven chip window. The processingof the fourth and eighth chips within the window, accordingly, providescoefficients to compensate for the distortion imparted by the three- andseven-chip delays of the second and third antenna signals.

The use of rake receivers to compensate for multipath distortion of aCDMA signal is disclosed in U.S. patent application Ser. Nos. 08/266,769and 08/871,109 which are incorporated herein as if fully set forth. Itwill be recognized to those who are of skill in the art that theutilization of a rake receiver or a vector correlator will providecompensation for not only multipath distortion, but also for the knowndistortion imparted by the multi-antenna system disclosed herein.

The gain of the signal output by the AMF is monitored by an automaticpower control (APC) which relays messages to the transmitting station tocontrol the power of the transmitted signal. Since the vector correlatoror rake receiver compensates for both multipath phase distortion as wellas the known distortion imparted by the antenna system, an enhanced gainis realized in comparison to a single antenna system where onlymultipath phase distortion is compensated for. Accordingly, therelatively higher gain which is received enables the APC to direct thetransmitting station to lower its power thus increasing the capacity ofthe overall CDMA system.

Where the physical site of the communication station requires or makesthe location of the antenna system desirable at a location relativelydistant to the processing components, applicants' have recognized thatsignificant loss in signal strength can occur. To address this problemthe receiver/transmitter (RxTx) may be physically separated from theother processing compartments. The RxTx may then be located in relativeproximity to the remotely located antennas and relatively distant to theprocessing modems. A significant improvement in signal strength is seenby the elimination of twenty feet or more of connecting cable betweenthe antenna system and the RxTx. Accordingly, where remote location ofthe antenna or antenna system is necessary, at least twenty feet ofcable is provided to couple the RxTx to the other signal processingequipment permitting the RxTx to be mounted in closer proximity andcoupled to the antenna system with a relatively short cable. Preferably,the signal coupling cable which connects the RxTx to the other signalprocessing equipment includes DC power to provide power to the RxTx.

Other aspects and advantages will become apparent to those skilled inthe art after reading the detailed description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a communication network embodimentof the present invention.

FIG. 2 is a schematic illustration of the propagation of signals betweena base station and a plurality of subscriber units.

FIG. 3 is a block diagram of a first embodiment of a communicationstation made in accordance with the teachings of the present invention.

FIG. 4 is a more detailed block diagram of a first embodiment of acommunication station made in accordance with the teachings of thepresent invention.

FIG. 5 is a schematic illustration of the vector correlator of thecommunication station shown in FIG. 4.

FIG. 6 is a schematic illustration of the phase locked loop of thecommunication station shown in FIG. 4.

FIG. 7 is a block diagram of a second embodiment of a communicationstation made in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Presently preferred embodiments are described below with reference tothe drawing figures wherein like numerals represent like elementsthroughout.

A communication network 2 embodying the present invention is shown inFIG. 1. The communication network 2 generally comprises one or more basestations 4, each of which is in wireless communication with a pluralityof subscriber units 6, which may be fixed or mobile. Each subscriberunit 6 communicates with either the closest base station 4 or the basestation 4 which provides the strongest communication signal. The basestations 4 also communicates with a base station controller 8, whichcoordinates communications among base stations 4. The communicationnetwork 2 may also be connected to a public switched telephone network(PSTN) 9, wherein the base station controller 8 also coordinatescommunications between the base stations 4 and the PSTN 9. Preferably,each base station 4 communicates with the base station controller 10over a wireless link, although a land line may also be provided. A landline is particularly applicable when a base station 4 is in closeproximity to the base station controller 8.

The base station controller 8 performs several functions. Primarily, thebase station controller 8 provides all of the operations, administrativeand maintenance (OA&M) signaling associated with establishing andmaintaining all of the wireless communications between the subscriberunits 6, the base stations 4, and the base station controller 8. Thebase station controller 8 also provides an interface between thewireless communication system 2 and the PSTN 9. This interface includesmultiplexing and demultiplexing of the communication signals that enterand leave the system 2 via the base station controller 8. Although thewireless communication system 2 is shown employing antennas to transmitRF signals, one skilled in the art will recognize that communicationsmay also be accomplished via microwave or satellite uplinks.

Referring to FIG. 2, the propagation of signals between a base station 4and a plurality of subscriber units 6 is shown. A two-way communicationchannel 11 comprises a signal transmitted 13 (TX) from the base station4 to subscriber station 6 and a signal received 15 (RX) by the basestation 4 from the subscriber unit 6. The signal between the basestation 4 and the subscriber unit 6 include the transmission of a pilotsignal. The pilot signal is a spreading code which carries no data bits.The pilot signal is used for synchronizing the transmission between thebase station 4 and subscriber unit 6. Transmission and reception of databegins after synchronization of the subscriber unit 6 and the basestation 4.

Referring to FIG. 3, a communication station 100, which may be either abase station 4 or a subscriber unit 6, includes an antenna system 110having a plurality of antennas 120, delay units 130 and a summer 135.The summer 135 is coupled to an RF receiver of a receiver/transmitter(RxTx) unit 140 via a cable 142. An RF transmit output of the RxTx 140is coupled to one of the antennas 120, preferably the first antenna, bya direction coupler 144 and connecting cable 146. The RxTx 140 isconnected to signal processing equipment 148 which includes one or moreof modems 150 via a cable 152. Preferably, the antenna system 110, RxTx140 and the other signal processing equipment 148 are in close proximityto each other to inhibit loss of signal strength. However, if it isnecessary to place the antenna system 110 in a location remote from thesignal processing equipment, for example more than 20 feet away,significant loss in signal level can result during transmission andreception. Applicants have recognized that the susceptibility to loss insignal strength can be significantly reduced by physically separatingthe RxTx 140 from the other signaling processing components 148including the modems 150 to permit a relatively short cables 142, 146 tocouple the RxTx and the antenna system 110 and a relatively long cable152 to couple the RF receiver 140 to the other processing equipment 148.Where separation of the units 140, 148 is desirable, preferably, thecoupling cable 152 is at least twenty feet long to permit a reduction inthe length of cables 142, 146 required to couple the RxTx 140 to theantenna system 110. To facilitate the location of the RxTx 140 inproximity with the antenna system 110, it is preferred that connectingcable 152 provide the DC power to the RxTx 140 from the other processingequipment 148 which includes modems 150. This may be accomplished byoverlaying the DC power on the signals to be transmitted.

Separate delay units 130 shift the time-of-arrival of the signalreplicas to the receiver. The resulting combined signal will have Ncopies of the received signal with different time delays wherein N is aninteger. Preferably, each delay unit 130 results in a delay of at leasttwo chips which enables further processing to achieve a net increase insignal strength.

The resulting combined signal is output by the summer 135 to the RFreceiver of the RxTx 140. The RF receiver of the RxTx 140 strips thecarrier frequency and passes a resulting baseband signal to the modems150. The signal received by each modem 150 has a distortioncorresponding to the delays imparted by the delay units 130. The signalsmay also have distortion attributable to multipath occurring naturallyin the channel 120.

As is known in the art, each CDMA communication is associated with aunique code. Multiple modems 150 enable simultaneous processing ofmultiple CDMA communications, each processing a communication associatedwith a different CDMA code. For subscriber units a single modem 150 maybe used if only a single communication is to be supported at any giventime. However, subscriber units may have several modems to supportmultiple communications or to serve as an emulated base station. Asexplained below, combining N signals with a known distortion enables thelowering of the transmit power required by the receiving units. As aresult, this increases the number of subscribers 6 or the number ofsimultaneous communications with a base station 4 within the system.

Referring to FIG. 4, a communication station 200 is illustrated havingan antenna system 205 containing three antennas 120, 120 a, 120 b, twodelay units 130 a, 130 b and one summer 135. This particularconfiguration permits an increase in up to 4.77 dB of gain in a receivedsignal as compared with a single antenna unit which receives a signaltransmitted at the same power. This gain translates into increasedcapacity (increased subscribers or increased number of simultaneouscommunications), which can be handled by communication station 200,since the transmit power can be reduced.

The three antennas 120, 120 a, 120 b are preferably spaced at least sixwavelengths apart, or equivalently, a few inches to a few yards fromeach other so that the antenna diversity gain is avoided by thearrangement. The antennas 120, 120 a, 120 b are preferably located so asto receive the CDMA communication signals from independent propagationpaths.

The summation unit 135 receives a signal from the first antenna 120 withno delay. The summation unit 135 receives a signal from the secondantenna 120 a via delay unit 130 a which imparts a delay of three chipsrelative to the first antenna's signal. The summation unit 135 alsoreceives a signal from the third antenna 120 b via delay unit 130 bwhich imparts a delay of seven chips relative to the first antenna'ssignal. The signal delay provided is typical, but can be changed by onehaving ordinary skill in the art, and is influenced by the temporalwidth of the vector correlator/rake receiver.

The delay units may comprise electronic circuitry, for example astanding acoustic wave (SAW) device, or simply be a selectively extendedpiece of cable coupling the antennas to the mixer 135, which isselectively extended to provide for desired delay. As explained below,benefits in increased gain are realized as long as the delays impartedare at least two chips and the vector correlator and/or rake receiverwhich analyzes the distortion has sufficient capacity to analyze the netdelays imparted by all of the delay units.

The signal from all three antennas 120, 120 a, 120 b are added by thesummer 135 then passed to an RF receiver 207 to strip the carrierfrequency. The resulting baseband signal has three copies of thereceived communication signal, each copy having a different delay.

The baseband signal output by the receiver 207 is processed by themodems 150. Delayed replicas of the communication signal are essentiallycombined by overlaying them with the correct phase and amplitude whichresults in increased gain. This function is performed by an adaptivematched filter (AMF) 250 which operates in accordance with filtercoefficients determined by a vector correlator 230 in conjunction with acarrier recovery phase lock loop 240. The three antenna system 110generally provides a gain of 3 to 4 dB and ideally 4.77 dB as comparedto a similar receiving station employing a single antenna. Therefore,there is generally a reduction of 3 to 4 dB in transmit power requiredto process communication.

The modem 150 includes an analog to digital converter 210 which convertsthe baseband signal into a digital signal with the assistance of atracker 220. The tracker 220 directs the digital converter 210 to samplethe strongest analog representation of the data being transmitted to thecommunication station 200 to provide an accurate digital signal. Thedigital signal includes both a digital data signal and a digital pilotsignal.

As is well known in the art, CDMA communication stations receive a pilotsignal to provide synchronization of a locally generated pseudo randomcode with the pseudo random code transmitted by the transmittingstation, and to provide a transmission power reference during initialpower ramp-up. Typically, a base station transmits the pilot signal toprovide synchronization of a locally generated pseudo random code withthe transmitted pseudo random code. The pilot signal is a sequence ofpseudo random complex numbers which are modulated in this system byconstant complex pilot value having a magnitude of one and phase ofzero.

The digital pilot signal will have the same phase distortion as thedigital data signal, since they are both contained within the basebandsignal. Accordingly, the vector correlator 230 receives the pilot signaland determines in conjunction with a phase lock loop 240, filtercoefficients based on the distortion of the pilot signal. Hence, thedetermined coefficients also represent the distortion of the datasignal. The data signal/CDMA communication signal, which is directed tothe adaptive match filter (AMF) 250, is processed by the AMF inaccordance with the filter coefficients generated by the vectorcorrelator in combination with the phase lock loop.

As disclosed in U.S. patent application Ser. Nos. 08/266,769 and08/871,109, vector correlators/rake receivers in conjunction with phaselock loop circuitry have been utilized to produce filter coefficients tocorrect for multi-path distortion. As used in the present invention, thevector correlator and phase lock loop generate filter coefficientsassociated with both natural multipath distortion and the artificiallyintroduced distortions imparted by the antenna system 130 a, 130 b, solong as the delays of the antenna system are within the correctionwindow used by the vector correlator 230.

Referring to FIG. 5, the vector correlator 230 provides an estimate ofthe complex impulse response, having real and imaginary components, ofthe channel over which the communication signal is transmitted includingthe antenna array in the present invention. The vector correlator 230has a plurality of independent elements 231.1, 231.2, 231 i, preferablyeleven, wherein the pilot pseudo random code input to each element isdelayed by one chip to define a processing window of eleven chips.

Each element 231 performs an open loop estimation of the sampled impulseresponse of the RF channel. Thus, the vector correlator 230 producesnoisy estimates of the sampled impulse response at evenly spacedintervals. The signal analysis performed by the vector correlator 230accordingly determines phase and amplitude distortions occurring atdifferent points within the processing window. Since known delays ofthree chips and seven chips have been imparted by delay units of 130 a,130 b, the vector correlator will determine the existence of copies ofthe signal at chip zero, chip three and chip seven. Where the receivedsignal also includes a five chip, for example, delayed replicaattributable to natural multipath, the vector correlator will determinesignal copies at zero, three, five, seven and eight chips. As will berecognized by those of ordinary skill in the art, providing the vectorcorrelator with a wider window, for example, twenty-one chips, wouldresult in the above example determining copies of the signal at zero,three, five, seven, eight and twelve. Preferably the vector correlatorhas a wide enough window to accommodate all of the delays imparted bythe antennas within the antenna system 205. In the above example, if thevector correlator processing window is less than eleven, the signalreceived by antenna 120 b will not be fully compensated for.

In operation, each element of the vector correlator 230 receives alocally generated pseudo random pilot code. The signal supplied to thevector correlator 230 from the analog digital converter 210 is input toeach element. Mixers 232 mix the locally generated pseudo random codewith the pilot to despread the pilot signal. Delay units 233 impart aone chip delay on the pilot code in all but one element 231. Eachelement 231 receives a carrier-offset-phase-correcting signal fromphased lock loop 240, which is mixed with the despread pilot signal ineach element 231 by mixers 233 to provide sample impulse responseestimates. The vector correlator 230 further includes a plurality of lowpass filters 234 which are connected to each mixer 233 and which smootheach corresponding sample impulse response estimate. The complexconjugates of each smoothed sampled impulse response estimate are usedas the filter coefficients or weights for the adaptive match filter 250.In addition, the complex conjugate of each smoothed sampled response ismixed with the despread pilot signal by mixers 235. The summation unit236 receives the outputs of mixers 235 and outputs the combined despreadpilot signal which is now corrected for multipath distortion.

The carrier recovery phase lock loop 240 acts upon the despread pilotsignal to estimate and correct the phase error due to RF carrier signaloffset. The offset may be due to internal component mismatches or tochannel distortion. Component mismatches between the subscriberoscillator and the receiver oscillator may cause slightly differentoscillator outputs. These component mismatches can be furtherexacerbated by local and environmental conditions, such as the heatingand cooling of electronic components, which may cause performancechanges in the components. With respect to channel distortion, dopplereffects caused by the motion of the receiving stations relative to thetransmitter station or a multipath reflector may cause the RF carrier tobecome distorted during transmission. This may also result in a RFcarrier offset.

The phase lock loop 240 is preferably implemented in a programmabledigital signal processor. The phase lock loop 240 monitors the output ofvector correlator 230 to estimate and correct for a phase error due toRF offset, thereby providing acceptable quality.

Referring to FIG. 6, the continuously adjusted-bandwidth PLL comprises amixer 241, a normalizing unit 242, and arctangent analyzer 243, a phasedlock loop filter 244, a voltage controlled oscillator 245 and abandwidth control section 246. The mixer 241 receives its input from thevector correlator 230 which is the despread pilot signal processed tocorrect for channel distortion due to multipath effects. The despreadpilot signal is mixed with a correction signal from voltage controlledoscillator 245 to produce a complex error signal, which is transmittedto normalizing unit 242. The normalized signal is then input intoarctangent analyzer 243. The output of the arctangent analyzer 243 is aquantized phase angle of the complex error signal. The bandwidth controlsection 246 continuously monitors the quantized phase error signal andgenerates a control signal to control the bandwidth of a phased lockloop filter 244. The signal output for the phased lock loop filter istransmitted to the voltage controlled oscillator 245. The voltagecontrolled oscillator 245 outputs a signal to mixer 241 and vectorcorrelator 230, which is indicative of a carrier-offset phase-error.This entire process is repeated until a complex error signal output fromthe mixer 241 is at a minimum. Optimum performance of the modem 150 willnot occur until the vector correlator 230 and phase lock loop 240 havereached a mutually satisfactory equilibrium point.

The vector correlator 230 outputs in conjunction with the carrierrecovery phase lock loop 240 filter coefficients to the adaptive matchedfilter 250. The adaptive matched filter 250 is then able to process thecommunication signal to compensate for channel distortion due to bothmultipath effects and the antenna system. This compensation increasesthe gain of the signal by, in effect, overlaying delayed replicas of thesignal. The adaptive matched filter 250 transmits the filtered resultingsignal to the traffic despreaders 260 and auxiliary despreader 270. TheAPC 290 determines whether the signal strength of the transmitted signalshould be increased or decreased to maintain an appropriate bit errorrate based upon the estimate of the signal strength resulting from thetraffic despreader 270. This information is transmitted from thecommunication station 200 to the station which transmitted the signal.

The traffic despreaders 260 transmit the despread filtered resultantsignal to the Viterbi decoder 280 which function as described incopending application Ser. No. 08/871,008 which is incorporated byreference as if fully set forth of the convolutional encoder (not shown)of a subscriber unit 6. The Viterbi decoder 280 passes the resultingsignal to a digital to analog converter 300 which provides for an outputto the user. For data communications, a digital output may be provided.

An alternative embodiment of the antenna system present invention isshown in FIG. 7. The antenna system 400 shown in FIG. 7 may besubstituted for the antenna system 205 shown in FIG. 4. The antennasystem 400 includes three antennas 410 a, 410 b, 410 c. The firstantenna 410 a is coupled to a first summer 450 by way of a firstbandpass filter 420 a, a first low noise amplifier 430 a and a firstdelay unit 440. A second antenna 410 b is coupled to the first summer450 by way of a second bandpass filter 420 b, a second low noiseamplifier 430 b and a first attenuator 460 b. The CDMA signals receivedby way of the first and second antennas 410 a, 410 b are summed bysummer 450 are then passed to a second summer 480 by way of a delay unit470. The third antenna 410 c is coupled to the second summer 480 by wayof a third bandpass filter 420 c, a third low noise amplifier 430 c anda second attenuator 460 c. A CDMA signal received by the third antenna410 c is summed with the output of the delay unit 470. Accordingly, theantenna system 400 outputs a signal including a known distortioncorresponding to the fixed delays imparted by the delay units 440 and470. It should be recognized by those of skill in the art that thisantenna system 400 achieves the same result as the antenna system 205shown in FIG. 4.

Although the invention has been described in part by making detailedreference to certain specific embodiments, such detail is intended to beinstructive rather than restrictive. It will be appreciated by thoseskilled in the art that many variations may be made in the structure andmode of operation without departing from the spirit and scope of theinvention as disclosed in the teachings herein.

What is claimed is:
 1. A CDMA base station comprising: a plurality ofselectively spaced omnidirectional antennas, each for receiving CDMAcommunication signals within the operating range of the base station; asummer associated with said antennas and having an output for outputtinga combined signal; a first of said antennas directly coupled to saidsummer; each subsequent antenna of said plurality of antennas associatedwith a respective delay unit, each respective delay unit being coupledto said summer and each respective delay unit imparting a differentfixed delay to the signal received by the respective antenna, each fixeddelay resulting in a delay of at least two chips relative to each otherdelay; the delayed signals being combined with the signal of said firstantenna by said summer, said combined output signal having a known phasedistortion corresponding to the fixed delays; a receiver coupled to theoutput of said summer; and a modem for receiving an individualcommunication signal associated with a unique CDMA code, said modemincluding distortion-compensating means for compensating for at leastsaid known phase distortion.
 2. The base station of claim 1 wherein saidantenna system includes three antennas, a second of said antennas beingassociated with a first delay unit which imparts a first delay to thesignal received by said second antenna, a third of said antennas beingassociated with a second delay unit which imparts a second delay to thesignal received by said third antenna whereby said known phasedistortion of said summer output corresponds to the predetermined delaysimparted by said first and second delay units.
 3. The base station ofclaim 2 wherein the delay imparted by said first delay unit results in athree chip delay and the delay imparted by said second delay unitresults in a seven chip delay.
 4. The base station of claim 3, whereinsaid modem includes a vector correlator for generating filtercoefficients for an adaptive matched filter based on signal distortiondetermined by said vector correlator; said vector correlator having aprocessing capacity of at least eleven chips whereby said vectorcorrelator compensates for said known distortion and for multipathdistortion ascertainable within its processing capacity; and saidadaptive matched filter processing communication signals with saidunique CDMA code using coefficients generated by said vector correlator.5. The base station of claim 4 wherein said modem further comprises anautomatic power control unit associated with said adaptive match filterfor generating a return power control signals for transmission.
 6. Thebase station of claim 2 wherein said antennas are spaced at least sixwavelengths apart from each other.
 7. The base station of claim 2wherein said antennas are spaced no more than three yards apart fromeach other.
 8. The base station of claim 2 wherein said receiver andsaid modem are located in physically separate units and furthercomprising a cable for coupling said modem to said receiver, said cableproviding power to said receiver.
 9. The base station of claim 8 whereinsaid cable is at least 20 feet long.
 10. A base station having anantenna system comprising: a plurality of single beam, omnidirectionalantennas, each for receiving CDMA communication signals within theoperating range of the base station; a summer associated with saidantennas and having an output for outputting a combined signal; a firstantenna of said plurality of antennas coupled to said summer; a firstdelay unit coupled to said summer and a second antenna of said pluralityof antennas for delaying and outputting said CDMA communication signalsfrom said second antenna; said summer combining said output from saidfirst delay unit and said signals received by said first antenna, saidcombined signal comprising at least two copies of the received signal bysaid plurality of antennas; and a modem for receiving an individualcommunication signal associated with a unique CDMA code within saidcombined signal.
 11. The base station of claim 10 further comprising areceiver coupled to said antenna system and said modem.
 12. The basestation of claim 11 wherein said combined signal further comprises aknown distortion corresponding to at least said first fixed delay. 13.The base station of claim 12 wherein each of said plurality of antennas,except said first antenna, is associated with a respective delay unitwhich is coupled to said summer.
 14. The base station of claim 13wherein said known distortion of said combined signal corresponds to allof said delay units.
 15. The base station of claim 14 wherein saidreceiver is a physically separate unit from said modem, and said basestation further comprises a cable for coupling said modem to saidreceiver including power conductors for supplying power from said modemunit to said receiver unit.
 16. The base station of claim 15 whereinsaid cable is at least 20 feet long.
 17. The base station of claim 10wherein said modem includes a vector correlator for generating filtercoefficients for an adaptive matched filter based on signal distortiondetermined by said vector correlator; said vector correlator having aprocessing capacity at least equal to a predetermined chip delaycorresponding to said known distortion whereby said vector correlatorcompensates for said known distortion and for multipath distortionascertainable within its processing capacity; and said adaptive matchfilter processing individual communication signals associated with saidunique CDMA code using coefficients generated by said vector correlatorwhereby increased signal gain is realized which is attributable in partto the compensation for said known distortion.
 18. The base station ofclaim 17 wherein said modem further comprises an automatic power controlunit associated with said adaptive match filter for generating powercontrol signal for transmission.
 19. The base station of claim 10further comprising: a plurality of modems coupled to said receiver, eachmodem for receiving an individual communication signal associated with aunique CDMA code, such that multiple communications received via saidreceiver can be simultaneously processed, each said modem includingdistortion compensating means for compensating for at least said knownsignal distortion.
 20. An antenna system for use in a CDMA base stationcomprising: first, second and third single beam, omnidirectionalantennas; each for receiving CDMA communication signals within theoperating range of the base station; a first summer coupled to saidfirst and second antennas, for combining said signals received by saidfirst and second antennas, whereby said combined signal comprises twocopies of the received signal; said first antenna coupled to said summerby way of a first delay unit; a second summer coupled to said firstsummer by way of a second delay unit, and coupled to said third antenna,for combining signals received by said third antenna with said combinedsignal output by said first summer and outputting a second combinedsignal; and a modem for detecting an individual communication signalassociated with a unique CDMA code within said second combined signal.21. An antenna system for use in a base station comprising: a pluralityof selectively spaced omnidirectional antennas, each for receiving CDMAcommunication signals within the range of the system; a summerassociated with said antennas and having an output for outputting acombined signal; a first of said antennas directly coupled to saidsummer; each subsequent antenna of said plurality of antennas associatedwith a respective delay unit, each respective delay unit being coupledto said summer and each respective delay unit imparting a differentfixed delay to the signal received by the respective antenna, each fixeddelay resulting in a delay of at least two chips relative to each otherdelay; the delayed signals being combined with the signal of said firstantenna by said summer, said combined output signal having a known phasedistortion corresponding to the fixed delays; and a modem for receivingan individual communication signal associated with a unique CDMA code,said modem including distortion-compensating means for compensating forat least said known phase distortion.
 22. The antenna system of claim 21further including three antennas, a second of said antennas beingassociated with a first delay unit which imparts a first delay to thesignal received by said second antenna, a third of said antennas beingassociated with a second delay unit which imparts a second delay to thesignal received by said third antenna, whereby said known phasedistortion of said summer output corresponds to the delays imparted bysaid first and second delay units.
 23. The antenna system of claim 22wherein the delay imparted by said first delay unit results in a threechip delay and the delay imparted by said second delay unit results in aseven chip delay.
 24. The antenna system of claim 23 wherein: said modemincludes a vector correlator for generating filter coefficients for anadaptive matched filter based on signal distortion determined by saidvector correlator; said vector correlator having a processing capacityof at least eleven chips whereby said vector correlator compensates forsaid known distortion and for multipath distortion ascertainable withinits processing capacity; and said adaptive match filter processingcommunication signals with said unique CDMA code using coefficientsgenerated by said vector correlator.